1. Field of the Invention
The present invention relates to a friction material, particularly relates to a friction material for an industrial machine, a railway vehicle, a baggage car, a passenger car, or the like, and more specifically relates to a friction material in a brake pad, a brake lining, a clutch facing, or the like, for use in the above-mentioned applications.
2. Description of the Related Art
In a friction material to be used mainly in a brake pad or the like, a fibrous reinforcement is used as one of materials for enhancing the strength of the friction material. Fibrous reinforcements used in place of asbestos fiber include glass fiber, steel fiber, aramid fiber, potassium titanate fiber, etc. Since these fibrous reinforcements have their own properties respectively, a mixture of several kinds of them is used.
Of these fibrous reinforcements, potassium titanate fiber is rated highly, as abrasive hard inorganic fiber, in the point that not only can it improve the strength, the heat resistance and the wear resistance of the friction material as a whole, but also it can enhance the friction coefficient of the friction material by its abrasive property, and particularly it can ensure a high friction coefficient at the time of a high load such as high-speed braking or the like.
However, potassium titanate fiber which has been used as alternative fiber to asbestos is composed of a needle-like single crystal having a diameter in a range of from 0.2 to 1 xcexcm and a length in a range of from 10 to 20 xcexcm, which is referred to as xe2x80x9cwhiskerxe2x80x9d. It is therefore undesirable on the working environment and sanitation to use such potassium titanate fiber.
It is therefore an object of the present invention to provide a friction material which uses no whisker-like potassium titanate fiber undesirable on the working environment and sanitation, but provides friction performance and strength equal to those with such whisker-like potassium titanate fiber while restraining the manufacturing cost from increasing.
In order to solve the foregoing problem, the present inventors carried out various researches on material qualities and forms of inorganic substances which use no whisker-like potassium titanate fiber undesirable on the working environment and sanitation, but provide friction performance and strength equal to those with such whisker-like potassium titanate fiber.
Thus, the present invention was developed taking account of the fact that, when powdery or flaky potassium titanate, which was no less potassium titanate than such whisker-like potassium titanate, was used, friction performance and strength equal to those with such whisker-like potassium titanate could be obtained.
That is, the present invention solved the foregoing problem by the following means.
(1) A friction material composed of a fibrous reinforcement, a friction modifier and a binder, wherein powdery or flaky potassium titanate with an aspect ratio of not higher than 3 is mixed as a friction material component.
(2) A friction material defined in the above item (1), wherein a diameter of the powdery or flaky potassium titanate is in a range of from 0.05 xcexcm to 150 xcexcm.
(3) A friction material defined in the above item (1) or (2), wherein fibrous potassium titanate which is a by-product when the powdery or flaky potassium titanate is produced and which has a length of not longer than 5 xcexcm or a diameter of not smaller than 3 xcexcm is mixed at a volume ratio of not higher than 30% with respect to the powdery or flaky potassium titanate.
(4) A friction material defined in any one of the above items (1) to (3), wherein the powdery or flaky potassium titanate is subjected to surface treatment with a silane coupling agent, phenolic resin, or the like.